where \(c_{i\sigma }\)  (\(c_{i\sigma }^\dagger \) ) annihilates (creates) a valence electron and \(n_{i\sigma } = c_{i\sigma }^\dagger c_{i\sigma }\)  is the number operator. The valence electrons form a single band with nearest-neighbor hopping amplitude \(t_\mathrm {h}\) , on-site Coulomb repulsion \(U\) , and nearest-neighbor interaction \(V\) . Although the formalism is general, we choose here model parameters capturing the physics of cuprate chain compounds such as Ba\(_{2-x}\) Sr\(_x\) CuO\(_{3+\delta }\) , namely \(U=8t_{\rm h}\)  and \(V=-t_{\rm h}\)  [1]}, [2]}. The ground state of EHM with these parameters at quarter filling was suggested to reside in proximity to a spin-triplet superconducting state [3]}, [4]}, [5]}, [6]}, [7]}, [8]}.
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